The present invention relates generally to the processing and bonding of polymer materials, and more particularly to the use of gas for the processing and bonding of polymer materials and polymer composite materials.
Polymer-based biomedical micro-/nanodevices containing environmentally sensitive biomolecules are attracting increased interest. The ability to assemble these devices at low temperatures in order to minimize denaturing is an important consideration. For instance, micro-arrays and microfluidic biochips need to be sealed with a lid, and the construction of three-dimensional tissue engineering scaffolds requires bonding of multiple two-dimensional layers with micro-/nanosized patterns. Processing and bonding of plastic materials usually require the use of either a temperature above the glass transition temperature (Tg) of the polymer substrates or organic solvents to deform solid materials so they can be molded into specific shapes or bond the material. For many applications, particularly biomedical products, high temperature and organic solvents may lead to denaturing of biomolecules. Residue of organic solvents is also a severe contamination. In micro- and nanoscale processing, applying heat and solvent alone may not be enough to guarantee high dimensional accuracy during fabrication of micro- or nanoscale features. In addition, heat and solvents tend to deform micro-/nanostructures.
During bonding, polymer interfaces undergo interfacial wetting, diffusion, and randomization stages. Diffusion of polymer chain segments across the interfaces and randomization of polymer chain segments determine the development of bond strength. Bonding of polymers at temperatures below their bulk Tg has been studied by several researchers. For example, polystyrene (PS) was bonded at Tg −41° C. or 62° C. and poly(2,6-dimethyl 1,4-phenylene oxide) (PPO) was bonded at Tg −126° C. or 90° C. using 100 μm thick polymer films. It was believed that this low temperature interfacial bonding resulted from the Tg depression in the proximity of polymer surfaces. Experimental observations of polymer thin films have shown that glass transition temperatures near the polymer surface differ from those in the bulk. The competition between the polymer-free surface and the polymer-substrate interactions determines this thickness-dependent Tg shift. When the polymer-free surface interaction dominates, the polymer shows a Tg depression with reducing thickness near the surface, typically less than 100 nm. An increase in Tg is observed as the thickness decreases when a strong interaction exists between the polymer chains and the underlying substrates.
However, literature results show that bond strength develops very slowly below Tg. As shown in Table 1, the bond strength of PS/PS at 62° C. with a PC of 0.8 MPa is only 0.08 MPa after 4 h. Even after 24 h, the bond strength is still low, 0.14 MPa, which is unsuitable for practical applications.
Therefore, there is a need for a method of bonding materials without using high temperatures, solvents, or adhesives.